The present invention relates to a recording and reproducing device, disk cartridge, and optical disk device, which can be used to record and reproduce information in high density, and in particular to a recording and reproducing device, disk cartridge, and optical disk for recording and/or reproducing a data signal with respect to a flexible optical disk.
Optical disks, such as a magneto-optical disk, have been widely used conventionally to record and reproduce information using a laser. In recent years, recording density of optical disks has been increasing to accommodate recording of more information. Along with this, optical disks have adopted smaller recording pits.
In order to read out information from such a high-density optical disk, the optical pickup needs to focus a light beam in such a way that the beam spot falls on a small domain of the optical disk where information is recorded. This makes it possible to read out information recorded in such a small domain. The smaller spot size enables recording of more information.
The spot size is proportional to wavelength xcex of the light source used, and is inversely proportional to numerical aperture NA of the objective lens. Thus, the spot size of a light beam can be reduced by either reducing the wavelength xcex of light from the light source, or by increasing the numerical aperture NA of the objective lens.
However, reducing the spot size by either of these methods causes large comatic aberration on the light beam when the optical disk tilts. The result of this is that the light beam cannot be accurately focused on the optical disk.
One conventional approach to solve this problem is to reduce thickness of the optical disk, and in turn length of optical path in the optical disk, so as to provide a larger margin of error for a tilt of the optical disk substrate.
For example, a CD-ROM has a numerical aperture NA=0.45, wavelength xcex=780 nm, and thickness of the optical disk substrate 1.2 mm. In contrast, a DVD-ROM has a numerical aperture NA=0.6, wavelength xcex=655 nm, and thickness of the optical disk substrate 0.6 mm. The DVD-ROM thus employs a light source which emits light of a shorter wavelength xcex, an objective lens with larger numerical aperture NA, and a thinner optical disk substrate, so as to increase recording capacity and a margin of error for a tilt of the optical disk substrate.
However, rigidity of the optical disk substrate weakens when the thickness of the optical disk substrate is further reduced to provide more margin of error for a tilt of the optical disk substrate. In fact, this only worsens the tilt of the optical disk substrate because weaker rigidity of the optical disk substrate causes the optical disk substrate to flutter. Therefore, there is a limit in reducing wavelength xcex of light of the light source and increasing numerical aperture NA of the objective lens.
In light of this problem, Japanese Unexamined Patent Publication No. 308059/1998 (Tokukaihei 10-308059) (published date: Nov. 17, 1998) teaches a recording and reproducing device which stabilizes rotation of an optical disk to allow for use of a thinner optical disk, an objective lens with larger numerical aperture NA, and light of a shorter wavelength xcex. FIG. 52 shows a structure of this recording and reproducing device.
As shown in FIG. 52, the recording and reproducing device is adapted to record and reproduce information with respect to an optical disk 401, by including a spindle 405 for rotating the optical disk 401, an optical pickup 403 for projecting and focusing a light beam on the optical disk 401, and an stabilizer 402 for stabilizing rotation of the optical disk 401. The optical disk 401 is very thin and flexible.
The optical disk 401 has a magnetic center hub 404 which fixes the optical disk 401 on the spindle 405 by magnetic coupling. The optical pickup 403 has focusing means such as a complex objective lens. The stabilizer 402 and the optical pickup 403 are disposed face to face on the both sides of the optical disk 401.
To record or reproduce information with respect to the optical disk 401, the optical disk 401 is rotated in the vicinity of the stabilizer 402. Here, a space of reduced pressure is created between the optical disk 401 and the stabilizer 402. Thus, the optical disk 401, being flexible, is drawn toward the stabilizer 402, and rotates at a constant distance from the stabilizer 402. As a result, fluttering of the optical disk 401 is suppressed, thereby recording and reproducing information in the recording and reproducing device with the optical pickup 103 having a wavelength of light not more than 650 nm and numerical aperture NA of the complex objective lens not less than 0.7.
Further, the foregoing publication also teaches a recording and reproducing device which uses a disk cartridge 406 integrally provided with the stabilizer 402, as shown in FIG. 53. In this case, the optical pickup 403 is inserted into the disk cartridge 406 through an opening (not shown) of the disk cartridge 406. The provision of the stabilizer 402 with the disk cartridge 406 suppresses fluttering of the optical disk 401 as in the recording and reproducing device of FIG. 52, thus realizing recording and reproducing of information with the thin optical disk 401, the objective lens with large numerical aperture NA, and light of short wavelength xcex.
Further, the foregoing publication discloses a structure in which a light beam is focused using a dual objective lens. For example, in a reproducing device shown in FIG. 54, a flexible optical disk 501, fixed on a center hub 503, is rotated by a spindle 504, so that the optical disk 501 is drawn toward the stabilizer 502 to stably rotate at a constant distance from the stabilizer 502.
A light beam 510 from a light source in a light emitting and detecting unit 505 is reflected at a mirror 506 and focused through the dual objective lens composed of a first objective lens 507 and a second objective lens 508 before it strikes the optical disk 501. The reflected light from the optical disk 501 is detected by a photodetector provided in the light emitting and detecting unit 505, so as to record or reproduce information with respect to the optical disk 501.
The dual lens is driven by a biaxial actuator 509 to carry out tracking and focusing. With such a reproducing device, a wavelength of light not more than 650 nm and numerical aperture NA of the dual lens not less than 0.7 can be realized.
However, the foregoing arrangement has the following problems.
Generally, recording and reproducing of information with respect to the optical disk employ a focus control whereby a constant distance is maintained between the optical disk and focusing means to maintain the laser beam in focus, so that the surface of the optical disk carrying the information is always within the depth of focus of the focusing means such as the objective lens.
In this manner, a focus control is carried out to record or reproduce information with respect to the optical disk 401. The optical pickup 403 approaches the optical disk 401. In this instance, in the arrangement of the foregoing publication, regardless of whether it is the recording and reproducing device of FIG. 52 or the recording and reproducing device using the disk cartridge 406 as shown in FIG. 53, the surface of the optical pickup 403 provided with the focusing means such as the objective lens is the surface facing the optical disk 401, which surface has relatively large irregularities. Thus, pressure fluctuates around the focusing means, or around the optical pickup 403, every time the focusing means is moved during a focus control, which causes fluctuation of air pressure between the optical pickup 403 and the optical disk 401. That is, the movement of the focusing means causes the optical disk 401 to flutter, which prevents stable focus control.
Further, in the reproducing device of FIG. 54, the flexible optical disk 501 fixed on the spindle 504 is rotated by the spindle 504 so that a space of reduced pressure is created between the flexible optical disk 501 and the stabilizer 502. The reduced pressure draws the optical disk 501 toward the stabilizer 502 so that the optical disk 501 stably rotates at a constant distance from the stabilizer 502. As a result, fluttering of the optical disk 501 is suppressed, thereby desirably recording or reproducing information.
However, because the dual objective lens which is disposed opposite the stabilizer 502 approaches the flexible optical disk 501 to reproduce information, the pressure between the dual objective lens and the optical disk 501 fluctuates. This causes the optical disk 501 to flutter (shudder) and thus prevent desirable recording and reproducing of information. Similarly, in the arrangement in which the disk cartridge is integrally provided with the stabilizer 502, desirable reproducing of information becomes difficult because the dual objective lens approaches the flexible optical disk 501.
Thus, one conventional problem is fluttering of the optical disk which is caused by pressure fluctuation around the optical disk, for example, due to movement of the focusing means of the optical pickup during a focus control. This means instable focus control, and therefore it was difficult to record and reproduce information desirably.
Another problem is that fluttering of the disk becomes more serious as the disk is rotated at higher speed, irrespective of whether the disk is flexible or not. It was therefore difficult to record and reproduce information stably.
An object of the present invention is to provide a recording and reproducing device, a disk cartridge, and an optical disk device, which can be used to record and reproduce information both stably and desirably with less fluttering, even at a high rotational speed, by suppressing fluttering of an optical disk by way of suppressing pressure fluctuation which is caused, for example, when an objective lens is moved.
In order to achieve this object, a recording and reproducing device of the present invention, in a recording and reproducing device which records and reproduces information by projecting a laser beam on a disk being rotated, comprises: a stabilizing slider which is disposed to face the disk and is supported to oscillate, a surface of the stabilizing slider facing the disk being flat.
According to this arrangement, rotation of the disk induces an air flow between the disk and the stabilizing slider, and air bearing is created between the stabilizing slider and the disk because the surface of the stabilizing slider facing the disk is flat. Further, since the stabilizing slider is supported to oscillate, the stabilizing slider can be moved in such a way that a constant distance is always maintained from the disk during rotation of the disk.
Thus, the disk rotates at a constant distance from the stabilizing slider. That is, fluttering of the disk is prevented even when the disk is rotating at high speed, thus stably recording and reproducing information.
Further, in order to achieve the foregoing object, in a disk cartridge of the present invention which contains a disk in a cartridge used in the recording and reproducing device, the disk being exposed when recording and reproducing information, the cartridge has inner wall surfaces which define a stabilizing board for creating a space of reduced pressure between the disk and the inner wall surfaces.
According to this arrangement, the stabilizing board defined by the both inner wall surfaces of the disk cartridge suppresses fluttering of the disk more effectively, thus realizing more stable and desirable recording and reproducing.
Further, in order to achieve the foregoing object, an optical disk device of the present invention, in an optical disk device which records and reproduces information with respect to an optical disk, comprises: rotation driving means for rotating an optical disk; a focusing unit for focusing light from a light source on the optical disk; a support member for supporting the focusing unit; and a rotation stabilizing board, fixed to the support member so as to be disposed between the focusing unit with the support member and the optical disk, for stabilizing rotation of the optical disk.
According to this arrangement, the rotation stabilizing board for stabilizing rotation of the flexible optical disk is provided on the focusing unit and the support member of the focusing unit. This prevents fluttering of the optical disk which may be caused when the focusing unit and the support member of the focusing unit are positioned in the vicinity of the optical disk. As a result, desirable recording and reproducing can be realized.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.